Maths help

Hi, i really want to do computer science in college however i need to get a B in maths GCSE. Only problem is i'm rubbish at maths(i got an E in my last test) I really want to be good at maths, can u guys give me suggestions on how to improve, and are there any good maths books i can learn from.

-I already practice and learn from khan academy-(i really need a good maths book to learn from the ground up to high level maths)